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javascriptchaining

How to chain in javascript yet get value in between

ok weird title, I know. However the question is simple. In a class I want to be able to do these two things:

invoice.getAmount(); // returns 1000

and

invoice.getAmount().asCurrency(); // returns $1000.00

I can do either, just don't know how to get both to work.

What I have for now for the second idea:

getAmount() {
 this._temp = this.amount;
 return this;
}

asCurrency(){
  if(this._temp){
    return "$" + this._temp + ".00";
  }
}

That's an ugly copy of what I really have but the concept is represented...

Any idea?

Thanks

Solution

  • Trick is to use the valueOf() method.

    class Invoice {

  constructor(value) {
    this.value = value;
  }

  getAmount() {
    return {
      valueOf: _ => this.value,
      asCurrency: _ => '$' + this.value
    }
  }
}

const i = new Invoice(150);

console.log(i.getAmount() + 10); // 160
console.log(i.getAmount().asCurrency()); // '$150'